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<h2><a name="SECTION007740000000000000000"></a><a name="comparison-to-builtin-set"></a>
<br>
5.7.4 Comparison to the built-in <tt class="class">set</tt> types
            
</h2>

<p>
The built-in <tt class="class">set</tt> and <tt class="class">frozenset</tt> types were designed based
on lessons learned from the <tt class="module">sets</tt> module.  The key differences are:

<p>

<ul>
<li><tt class="class">Set</tt> and <tt class="class">ImmutableSet</tt> were renamed to <tt class="class">set</tt> and
      <tt class="class">frozenset</tt>.
</li>
<li>There is no equivalent to <tt class="class">BaseSet</tt>.  Instead, use
      <code>isinstance(x, (set, frozenset))</code>.
</li>
<li>The hash algorithm for the built-ins performs significantly better
      (fewer collisions) for most datasets.
</li>
<li>The built-in versions have more space efficient pickles.
</li>
<li>The built-in versions do not have a <tt class="method">union_update()</tt> method.
      Instead, use the <tt class="method">update()</tt> method which is equivalent.
</li>
<li>The built-in versions do not have a <tt class="method">_repr(sorted=True)</tt> method.
      Instead, use the built-in <tt class="function">repr()</tt> and <tt class="function">sorted()</tt>
      functions:  <code>repr(sorted(s))</code>.
</li>
<li>The built-in version does not have a protocol for automatic conversion
      to immutable.  Many found this feature to be confusing and no one
      in the community reported having found real uses for it.
</li>
</ul>    

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<span class="release-info">Release 2.5.1, documentation updated on 18th April, 2007.</span>
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